A display apparatus that displays an image such as a liquid crystal display has a light control unit that controls a light transmittance and a light irradiation unit that supplies light to this light control unit. Among these, the light control unit corresponds to an LCD (Liquid Crystal Display) or the like, and the light irradiation unit corresponds to a back light such as an LED (Light Emitting Diode).
Herein, the light irradiation unit controls a light emitting amount in accordance with the largest luminance among respective luminances included in input images. Also, the light control unit controls the light transmittance on the basis of the respective luminances of the input images. To be more specific, the light control unit sets a high light transmittance for an area having a high luminance among the input images and displays the relevant area in a bright manner. On the other hand, by setting a low light transmittance for an area having a low luminance in the input image, the light control unit interrupts excess light and displays the relevant area in a dark manner. As the light irradiation unit and the light control unit operate in this manner, even when the area having the high luminance and the having the low luminance exist in a mixed manner in the input image, it is possible to appropriately display the input image in accordance with the respective luminances.
However, as a response speed of the light control unit is slower as compared with a response speed of the light irradiation unit, the control on the light transmittance by the light control unit may not manage to track a change in the light emitting amount by the light control unit, and a problem occurs that flicker is generated on a screen. This flicker is generated in an area other than an area having the largest luminance among the input images. In the following description, the area other than the area having the largest luminance is referred to as flat section.
FIG. 22 and FIG. 23 are explanatory drawings for describing the flicker generated in the flat section. FIG. 22 illustrates a relation between the light emitting amount with respect to the flat section, the light transmittance with respect to the flat section, and the luminance in the flat section in a case where the display apparatus displays input images is to is in the order of the input images 1a, 1b, and 1c. It is supposed that the input images 1a and 1c do not include images having a high luminance, and the input image 1b includes an image having a light luminance at one part. Also, a graph on the first stage from the top represents a time change in the light emitting amount with respect to the flat section, in which the vertical axis represents the light emitting amount, and the horizontal axis represents the time. A graph on the second stage from the top represents a time change in the transmittance with respect to the flat section, in which the vertical axis represents the transmittance, and the horizontal axis represents the time. A graph on the third stage from the top represents a time change in the luminance with respect to the flat section, in which the vertical axis represents the luminance, and the horizontal axis represents the time.
As illustrated in FIG. 22, the display apparatus sets the light emitting amount as 1A at a timing of displaying the input image 1a and sets the light emitting amount as 1B at a timing of displaying the input image 1b. Furthermore, the display apparatus sets the light emitting amount as 1A at a timing of displaying the input image 1c. The light emitting amount 1B is set to be larger than the light emitting amount 1A. On the other hand, to keep the luminance in the flat section as 1E, the display apparatus controls the light transmittance in accordance with the change in the light emitting amount. That is, while the light emitting amount is 1A, the transmittance is set as 1C, and at a moment when the light emitting amount becomes 1B, the transmittance is set as 1D. The transmittance 1C is set to be larger than the transmittance 1D.
A speed at which the transmittance is changed from 1C to 1D is slower than a speed at which the light emitting amount is changed from 1A to 1B. Thus, the display apparatus may not manage to interrupt the light from the light irradiation unit, and a flicker 1Ea is generated. The flicker 1Ea becomes “flicker seen bright for a moment” for viewers. Also, a speed at which the transmittance is changed from 1D to 1C is slower than a speed at which the light emitting amount is changed from 1B to 1A. The display apparatus may not increase the transmittance in accordance with a decrease in the light emitting amount and may not supply sufficient light. Thus, a flicker 1Eb is generated. Such flicker 1Eb becomes “flicker seen dark for a moment” for the viewers.
FIG. 23 illustrates a relation between the light emitting amount, the light transmittance in the flat section, and the luminance in the flat section in a case where the display apparatus displays input images 2a to 2c in the order of the input images 2a, 2b, and 2c. It is supposed that the input images 2a and 2c include images having a light luminance at one part, and the input image 2b does not include images having a high luminance. Also, a graph on the first stage from the top represents a time change in the light emitting amount with respect to the flat section, in which the vertical axis represents the light emitting amount, and the horizontal axis represents the time. A graph on the second stage from the top represents a time change in the transmittance with respect to the flat section, in which the vertical axis represents the transmittance, and the horizontal axis represents the time. A graph on the third stage from the top represents a time change in the luminance with respect to the flat section, in which the vertical axis represents the luminance, and the horizontal axis represents the time.
As illustrated in FIG. 23, the display apparatus sets the light emitting amount as 2B at a timing of displaying the input image 2a and sets the light emitting amount as 2A at a timing of displaying the input image 2c. Furthermore, the display apparatus sets the light emitting amount as 2B at a timing of displaying the input image 2c. On the other hand, to keep the luminance in the flat section as 2E, the display apparatus controls the light transmittance in accordance with the change in the light emitting amount. That is, while the light emitting amount is 2B, the transmittance is set as 2D, and at a moment when the light emitting amount becomes 2A, the transmittance is set as 2C.
A speed at which the transmittance is changed from 2D to 2C is slower than a speed at which the light emitting amount is changed from 2B to 2A. The display apparatus may not increase the transmittance in accordance with a decrease in the light emitting amount and may not supply sufficient light. Thus, a flicker 2Eb is generated. Also, a speed at which the transmittance is changed from 2C to 2D is slower than a speed at which the light emitting amount is changed from 2A to 2B. The display apparatus may not manage to interrupt the light from the light irradiation unit, and a flicker 2Ea is generated.
When the flickers are generated simultaneously or continuously in the flat section, the image is degraded. For example, Japanese Patent Application Publication No. 2005-258403 and Japanese Patent Application Publication No. 2006-147573 disclose technologies for dealing with slack of a response of the light control unit by imposing a limit on a change in the light amount of the light supplied by the light irradiation unit to moderate the change in the light emitting amount with respect to the time change for suppressing the flickers.
According to technologies disclosed in Japanese Patent Application Publication No. 2005-258403 and Japanese Patent Application Publication No. 2006-147573, flicker is suppressed by moderating a change in a light emitting amount with respect to a time change.